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Solutions to Chapter 5
1. Explain the difference between connectionless unacknowledged service and connectionless acknowledged service. How do the protocols that provide these services differ?
Solution:
In an acknowledged connectionless network, reliable delivery can be achieved through the use of
ACK and NAK transmissions. Such protocols are suited for communication over networks in which higher layers are sensitive to loss and the underlying network is inherently unreliable with a significant probability of loss or error.
Unacknowledged networks provide simpler and faster communication for networks that are inherently reliable or provide service to higher layers that can tolerate information loss.
2. Explain the difference between connection-oriented acknowledged service and connectionless acknowledged service. How do the protocols that provide these services differ?
Solution:
The use of acknowledgments can provide reliable transfer over networks that are prone to error and loss. In connection oriented networks, every packet in a data flow travels on the same path through the network and the proper ordering of packets is guaranteed. In such networks, if a packet arrives out of order, the receiver immediately knows that a packet has been lost. In a connectionless network, the service needs a mechanism for dealing with unordered delivery of information. This is especially important for real-time or delay-sensitive traffic, which may require immediate retransmission and may not be able to use buffering to correct unordered packet arrivals.
3. Suppose that the two end-systems α and β in Figure 5.3 communicate over a connection-oriented packet network. Suppose that station α sends a 10-kilobyte message to station β and that all packets are restricted to be
1000 bytes (neglect headers); assume that each packet can be accommodated in a data link frame. For each of the links, let p be the probability that a frame incurs errors during transmission.
1. Explain the difference between connectionless unacknowledged service and connectionless acknowledged service. How do the protocols that provide these services differ?
Solution:
In an acknowledged connectionless network, reliable delivery can be achieved through the use of
ACK and NAK transmissions. Such protocols are suited for communication over networks in which higher layers are sensitive to loss and the underlying network is inherently unreliable with a significant probability of loss or error.
Unacknowledged networks provide simpler and faster communication for networks that are inherently reliable or provide service to higher layers that can tolerate information loss.
2. Explain the difference between connection-oriented acknowledged service and connectionless acknowledged service. How do the protocols that provide these services differ?
Solution:
The use of acknowledgments can provide reliable transfer over networks that are prone to error and loss. In connection oriented networks, every packet in a data flow travels on the same path through the network and the proper ordering of packets is guaranteed. In such networks, if a packet arrives out of order, the receiver immediately knows that a packet has been lost. In a connectionless network, the service needs a mechanism for dealing with unordered delivery of information. This is especially important for real-time or delay-sensitive traffic, which may require immediate retransmission and may not be able to use buffering to correct unordered packet arrivals.
3. Suppose that the two end-systems α and β in Figure 5.3 communicate over a connection-oriented packet network. Suppose that station α sends a 10-kilobyte message to station β and that all packets are restricted to be
1000 bytes (neglect headers); assume that each packet can be accommodated in a data link frame. For each of the links, let p be the probability that a frame incurs errors during transmission.